This invention relates to an apparatus for warning of the abnormality of an engine when lubricating oil becomes less than predetermined quantity.
In general, an industrial utility engine is provided with a device which always monitors the quantity of the lubricating oil and stops the engine or turns on an alarm lamp to prevent the engine from burning when the oil becomes low.
However, it is difficult to stop the engine and further turn on the alarm lamp only by a magneto which produces minute current. Furthermore, the device should be arranged for various purposes and needs of operators. For example, when the engine is installed with a generator which is mounted on a specific location, the engine should be stopped immediately after the shortage of the oil is detected.
For another example, such an engine as installed on a golf cart requires only alarming without being stopped because the cart cannot run. However, cost for production will increase if the device is rearranged according to various purposes.
Japanese Patent Laid-open Nos. 62(1987)-93417 and -26379 disclose a float switch-type sensor and a lubricating oil pressure-type sensor respectively for detecting the shortage of lubricating oil. However, the float switch-type sensor should be dipped in the oil of an oil pan. Therefore, it is difficult to keep the sensor in good condition. On the other hand, the pressure-type sensor cannot be used for a natural lubrication-type engine but only for a forced-feed lubrication-type engine.
Recently, a sensor which has two electrodes disposed in an oil pan at a threshold level representing the shortage of lubricating oil has been developed. Therefore, the value of the resistance across the electrodes becomes so large when there is the shortage of lubricating oil. However, the lubricating oil has such a characteristic that its insulative resistance is gradually lowered with increase of temperature. (This will be explained later.)
This causes misjudgment that the engine has a shortage of lubricating oil even though the lubricating oil is enough. Such misjudging also happens when the electrodes are exposed to air due to wave motion of the lubricating oil.